Find all pairs of prime numbers with , for which both numbers and are also prime.
Solution
For the number to be prime the numbers and must be of different parity, which automatically means that , since . By the problem statement we then have that the numbers , and should be prime. Since they obviously have different remainders in division by , one of them must be equal to . So we have three possibilities:
* If , then , , and the pair satisfies the problem statement;
* if , then , and is not prime;
* if , then , and is not prime.
So after considering all possible cases we end up with a single solution .
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